Obesity is a growing major medical problem worldwide. It is the second most important cause of preventable death in the US, exceeded only by cigarette smoking. Current treatments consist of diet, exercise, behavior modification, surgical intervention, and pharmacological intervention alone or in combination. However, long-term success rates are poor, and thus there is a major unmet need for new approaches to treat obesity. The overall goal of this proposal is to develop a novel peptide termed lipid mobilizing factor (IMF) as a therapy for obesity. LMF was discovered in the urine of humans undergoing weight-loss diets based on its ability to stimulate lipolysis in cultured adipocytes. The first aim is to completely purify LMF and determine the amino acid sequence. This will be accomplished using standard chromatographic procedures for protein purification. After purification and identification of LMF, synthetic LMF will be prepared by standard peptide synthesis procedures. Synthetic LMF will be tested along with natural purified LMF to confirm activity in vitro. The peptides will be tested for stimulation of lipolysis in murine 3T3-L1 adipocytes and in human adipocytes. After the activity of synthetic LMF has been confirmed in vitro, it will be tested in an animal model of obesity. Mutant diabetic (db/db) mice overeat and become obese because they cannot respond to the satiety-inducing hormone, leptin, due to a mutation in the leptin receptor. Starting at six weeks of age, mice will be given injections of synthetic LMF or vehicle control and will be monitored for weight gain and food and water consumption for two months. Based on previous results, it is expected that LMF will significantly inhibit weight gain, probably due to an increase in energy expenditure. After two months, animals will be sacrificed and the body composition analyzed to determine if inhibition of weight gain is due to a decrease in fat or lean body mass. If LMF inhibits weight gain due to a decrease in fat mass, this will justify further evaluation in phase II studies including different animal models of obesity, pharmacology, and toxicology, and analysis of mechanism of action. The results of this investigation may provide a new approach to treat obesity.